Salmon and Protected Areas

Adelaide Robinson

Background and Motivation

  • Many populations of anadromous salmon are expected to go extinct within the next 100 years

    • Anadromous fish are born in freshwater, migrate to ocean and return to freshwater to reproduce
    • Most steelhead and all coho populations within California Are Federally listed
  • Habitat loss and urban land use are linked with their decline and lowered juvenile survival

Question

How do protected areas impact salmon populations within California?

Data

  • California Monitoring Plan for Salmon and Steelhead

    • CDFW and NOAA

    • Monitor and Assemble data on anadromous salmon populations across CA

      • Adult population counts

      • Geospatial data containing the extents of monitored watersheds

  • California Protected Area Database

    • Polygons of areas protected for open space across CA

Data Wrangling

Analysis

\(population = B_0 + B_1year_i + B_2PercentProtected_i + B_3year_i * percentprotected_i +E_i\)

  • OLS Linear Regression

    • Multiple Regression: Population regressed on percent protected and year
    • Interaction: Percent protected and year
      • The slope of the relationship between year and population count can vary based on %protected.
  • \(H_0: B_1 = B_2 = B_3 = 0\)

  • \(H_A: B_1 ≠B_2 ≠B_3 ≠ 0\)

  • Ran analysis for Both coho salmon and steelhead

Results

term estimate std.error statistic p.value conf.low conf.high
(Intercept) -729.154459 402.4470207 -1.811802 0.0703888 -1519.1223835 60.8134660
percent_protected 14.830868 6.2720549 2.364595 0.0182859 2.5193783 27.1423570
year 35.368786 12.3969912 2.853014 0.0044416 11.0345881 59.7029838
percent_protected:year -0.464231 0.1962358 -2.365679 0.0182328 -0.8494246 -0.0790375

Interpretation

  • Watersheds with higher numbers of percent protected have higher numbers of fish

    • when year is 0 there will be on average 14 more steelhead for each one unit increase in percent protected
  • Increase in percent protected decreases the rate of change in populations over time

    • -0.5 is the difference in the effect of year on steelhead count for every one increase in protected area
  • Steelhead are increasing over time

    • when percent protected is 0 on average there will be an increase of 35 fish per year
  • Coefficients are statistically significant using a significance level of 0.05, except the intercept.

Limitations and OLS Violations

  • True population likely not linear in parameters

  • Is there omitted variable bias?

  • Error is not normally distributed or independent

Lessons and Next Steps

  • Although my results were significant, I fail to reject the null due to concerns over OLS violations

    • Other methods besides OLS may be better for answering my question
  • Explore the relationship between protected areas and survival in a different way

    • Would be better to look at overwinter survival rate